Method of brazing and brazing alloy



Patented Nov. 17, 1953 I 7 ;:z,s59,1ss- 1 imnonorinnszmo Ami BRAZING ALLQY Pliilip St'roup, New Kensington,"Pa., ass'lgnor ato Aluminumt'Company of America, Pittsburgh, 1%., a corporation of' Pennsylvania NoIDna viIng; Application m rshal-110,19,

'- "Serial No. 64,699

This invention relates to an improved icompossi-tion of matter particularly useful'iinzthe brazing -'of-:raluminous materials, the latter :term being -nse'd to designate :aluminum :and alloys thereof which contain more :than :50 ipier cent of that imetal. The invention also,=contemplates' novel methods of brazing aluminous material. The :problems to which the "invention relates, :and to which it ofierstat ile'ast a partial solution, are zfundamental -to brazing compositions used in the :brazi-ng -.of alum-inous' material and arise -from :the fact ;-that the joint formed by brazing the aluminous parts is usually the portion of the completed brazed article leastrresistant to corrosion and Lfrom the further fact that the brazing composition should have a melting point low rcnough that the temperature necessarily used to {placieit "in a molten state will notjbe so high to permanently impair ithegphysicai properties of -the aluminous ,parts which arefto be joined bythebrazingoperation. 'Thus thejper'fect com- .position for brazing aluminous materials would be one whichfmelted at aivery low temperature and likewise "possessed a resistance to corrosion equal to "that of the aluminousmaterials 'which "were to The 'jo'ined'by the brazing operation. 'In orderto satisfy 'the requirement of corrosion resistance it is necessary to .use a brazing compositionhav'ing an aluminum base, butgalum'inum having a -rlatively high melting point, it is likewise necessary to add to that metal elements which will reduce its melting EDOll'lt. addistion oij such elements produces an alloy having a conrosionrresistance less thanthat of pure :aluminum so that, in the end, thebrazing composition is, at best, a compromise.

The obj ect-of this --in'vention is -to' provide brazsing walloys for use in {the bra zing of ialuminous ;'-materials which {13055658 to a superiorextent ;the desirable properties of high corrosion resistance --.=a nd ilow.;melting rpoint." 1'

To this end I provide 'an-improved brazing .iccm c tion i h r w s es e cons of aluminum, silicon and germanium, :the silicon being present in amounts of about 1.5 to about 12 per cent by weight and the germanium being present in amounts of about 3.5 to about 47 per cent by weight and the balance being aluminum of a purity hereinafter discussed. The invention is based on my discovery that'the conventional and widely usedbrazing compositions consisting essentially of aluminum and silicon are greatly improved by the addition of germanium, the improvement consisting in a substantial lowering of the meltin point of the composition without sub- .f i iq n'a icia i e, H

rmai u h r ix e s nts n nib i c less thanabout *l *and'hot greaterthana'bou'tIOffi."

sitiontlirnits .ab

stantial decrease in the corrosion resistance of the composition. Aluminum-silicon alloys have l'heretofore been widely used as "brazing alloys "However, such added elements "haire -sharply decreased'the corrosion resistance-of the aluminumsilicon alloy; The newcomposition ofthis invention is substantially as =resistant to corrosion 'as the aluminum-silicon allo-ye but substantially lower in melting point, the alloys of this invention melting within :a rangeo'f -about 800to ll'050 An additional advantage of my new brazing I-compositions is :the fmanner in which &.they when :held at'ztemperatures immediately above theirmelting ipoint. 5A1; such temperatures ithese compositions are "very ifillld and rare rcapable'zof entering comparativelyzsnrall intersticesrorzspaces.

This ipmperty .is of great :importance :brazing operationswhere the=parts ato zbed razed are posiitioned- -.slightly apart from each jcither a-n'd the -zmoltenrbrazingicemposition fiowed-iintoatheispaces defined by adjacent surfaces of said parts. The

rfiow characteristics of the compositions ;,of this invention are such that the space -:b etwe en the brazed parts may be reduced, :thu's :reducing-ithe -amount ofqbrazing composition necessarily :used and h ebrn r a t e e at e ro ion i-sistance of the .joint.

While-theadvantags just=describedare ltypical of the alloys .of this invention within the compoove'. indicated l have ,found that positionfli'mitsithere arela sefies ofanbys wmc v fl s tha m wei h contain about 1115 minus X'gpe ce REX-per These series of alloys possess an exceptional combination of low melting point, fluidity and resist-.

ance to corrosion and are preferred among the alloys within the scope of this invention as brazing alloys in the brazing of aluminous materials. I prefer, to the extent commercially feasible,

"to limit the composition of the alloy to aluminum,

germanium and silicon, but such metals are-hot commercially obtainable in pure form and some other metals'or metalloids will always-be present to some extent. Occasionally, it may likewise be desirable to add other metals or metalloids. I have found that for best results it is desirable to so limit the amount of metals or metalloids, other than the aluminum, germanium and silicon, that in total amount they do not exceed about 0.5 per cent by weight of the total alloy. I have also found it desirable to. limit those of these elements which melt at temperatures over 2000 F., e. g., iron, manganese, titanium, chromi-- um, to not greater than about 0.25 per cent by weight of any one. The alloy is, therefore, substantially free from any substances that might obstruct its flow under brazing conditions. Thus the most desirable alloys of the type herein d8! scribed contain a total of at least about 99.5 per U cent by weight of aluminum, germanium and silicon and thus consist essentially of those metals. 7

In the aluminum, silicon, germanium alloys above described there often occur small amounts of relatively low m-eltingconstituent. The presence of this constituent in many cases may be disregarded. However, where it is desirable that during brazing the brazing alloy melt within a minimum melting range, the low melting constituent may be eliminated by preheating the brazing alloy at temperatures between 760 and the solidus temperature, preferably below 900 F.,

prior to its use. To this end heating necessary to Q eflect substantial elimination of the relatively low melting constituent will vary with the dimensions of the brazing alloy article being heated,

butmayreadily be determined by trial. Usually the desired effect is produced by heating at the above indicated temperatures for a period over 30 minutes.

' The heating step above described, if conducted within the temperature: range of 760780 F.,

may likewise be advantageously used when the assembly formed by the brazing operation is intended for use at relatively high temperatures.

vIn this case the assembly, after brazing, is subjected to the above described heating step, thereby insuring the elimination of low melting constituent at the brazed joint and substantially eliminating the possibility of joint weakness due to incipient fusion of low melting constituent therein This application is a continuation-impart of my copending' application Serial No. 647,651 filed February 14, 1946, now abandoned.

Having thus described my invention, I claim: 1. Inthe method of brazing aluminous articles in which the joining .of adjacent surfaces is.

accomplished by the fusion and subsequent j solidification of brazing alloy therebetween, the

improvement consisting in utilizing thereinxas the brazing alloy ametallic composition composed essentially of the elements silicon, germanium and aluminum, s'aid elements composing'at least 99:5 per cent. by weight of the total com- .position,.the percentage of silicon by weight being equal to 11.5 minus X, and the percentage of 4 germanium by weight being equal to 4.5x, where X represents a number of 1 to 10.5 inclusive.

2. In the method of brazing aluminous articles in which the joining of adjacent surfaces is 5 accomplished by the fusion and subsequent solidification of brazing alloy therebetween, the

} improvement consisting in utilizing therein as a brazing alloy a metallic composition, 99.5 per cent of the total weight of which is composed of the elements aluminum, silicon and germanium, the element silicon composing about 1.5 to about 12 per cent by weight of said composition and the element germanium composing about 3.5 to about 47 per centby weight of said composition.

3. The process of claim 2 characterized by the fact that said brazing alloy is preheated within j the range of 760 F. to its solidus temperature prior to said fusion thereof between said surfaces,

said preheating extending over a sufiicient length of time to eliminate any low melting point constituent.

4. The process of claim 2 characterized by the fact that after solidification of said brazing alloy between said surfaces the resultant brazed assembly is heated for at least minutes within-a temperature range of about 760 F. to about 780 F.

5. A brazing alloy composed essentially o silicon, germanium and aluminum and containing not more than about 0.5 per cent by weight of other metal or metalloid, the percentage of silicon by weight being about equal to 11.5 minus X and the percentage of germanium by weight being about equal to 4.5K where X represents a References Cited in the file of this patent UNITED STATES PATENTS I Number Name Date 500,125 Guttner June 27, 1893 2,359,926 McCullough Oct.'10, 1944 2,386,889 Furry 1 ..7 Oct. 16,1945 2,508,008 Block May 16, 1950 OTHER REFERENCES Transactions of The Electrochemical Society, Vo1. '89 (1946), pp. 277, 278, and 288. "(Copy in "mused e Chem.'Abstracts, vol. 34 (-1940), p. 7764. (Copy in Scientific Library.) 7 7 Metall and Erz., v01. 25 (1926), pp. 6 2-634.

Q (Copy in Scientific Library.) 

5. A BRAZING ALLOY COMPOSED ESSENTIALLY OF SILICON, GERMANIUM AND ALUMINUM AND CONTAINING NOT MORE THAN ABOUT 0.5 PER CENT BY WEIGHT OF OTHER METAL OR METALLOID, THE PERCENTAGE OF SILICON BY WEIGHT BEING ABOUT EQUAL TO 11.5 MINUS X AND THE PERCENTAGE OF GERMANIUM BY WEIGHT BEING ABOUT EQUAL TO 4.5X WHERE X REPRESENTS A NUMBER NOT LESS THAN ABOUT 1 NOR GREATER THAN ABOUT 10.5. 